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falconia has posted comments on this change by falconia. (
https://gerrit.osmocom.org/c/libosmo-netif/+/39280?usp=email )
Change subject: bring twjit into libosmo-netif
......................................................................
Patch Set 5:
(1 comment)
File src/twjit.c:
https://gerrit.osmocom.org/c/libosmo-netif/+/39280/comment/62e74621_c69d26c… :
PS2, Line 504: rtph = osmo_rtp_get_hdr(msg);
Thanks. After having read your document: […]
I
still disagree. To see why, let us consider a scenario in which you (presumably) believe
checking M bit would make a difference. This purported scenario would have to have these
two properties:
* SSRC stays the same, or else twjit would consider it a handover;
* All timestamp increments are integral multiples of 160, for the same reason;
* Sequence number does not matter at all, as twjit does not look at it except for
staff-oriented counters and RTCP-mandated analytics - it does not affect any of
twjit's actual decisions.
With the above prerequisites established, the next question is: gap or no gap? Consider
the no-gap case first: there is a perfectly smooth, uninterrupted flow of RTP packets, but
one of them has M bit set. With current code, this smooth packet flow will be delivered to
the fixed timing application perfectly in order, without any disruptions - and I argue
that this behavior is the best. Your proposal of treating M bit as handover would cause
twjit state transition to HANDOVER, which would result either in some packets before the
handover event being dropped if the new flow becomes ready (flow start criteria) soon
enough, or in a gap (not present in the incoming stream) being fed to the output if the
old flow underruns before the new one is ready. How would such behavior be any better than
what I have currently?
Now consider M bit preceded by a gap: some packets omitted, then an RTP packet with M bit
set. Here the question becomes: underrun or no underrun? If the gap is long enough for
twjit to experience an underrun before the flow resumes, then it makes no difference
whether the flow-resuming packet has M bit set or not: twjit is starting from EMPTY state
in this case. Now consider the no-underrun case: the configured buffer depth is high
enough, and the gap short enough, to where the flow-resuming packet arrives before the
buffer underruns. With my current algorithm, the duration of the gap delivered to the
fixed timing application will be exactly what the RTP sender indicated in its timestamps;
with your proposed modification, the gap would be unpredictably lengthened or shortened
based on how long it takes for the post-handover flow to reach ready state. How is your
way any better?
In summary, I still fail to see *even one* scenario in which your proposed modification to
my core algorithm would make an improvement.
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Gerrit-MessageType: comment
Gerrit-Project: libosmo-netif
Gerrit-Branch: master
Gerrit-Change-Id: Ia3be5834571ca18b68939abbcf1ce3a879156658
Gerrit-Change-Number: 39280
Gerrit-PatchSet: 5
Gerrit-Owner: falconia <falcon(a)freecalypso.org>
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